1. Field of the Invention
This invention relates to an attenuated mutant of Pasteurella haemolytica, biotype A, serotype 1 which is useful as a vaccine against bacterial respiratory disease in cattle.
2. Prior Art
A leading cause of bacterial respiratory disease in cattle is P. haemolytica. The disease is particularly contagious when animals are accumulated, such as prior to or during shipping. Monetary losses attributable to death, weight loss, lost milk production and treatment are estimated to be several hundred million dollars annually.
Various prior art vaccines have been developed for P. haemolytica with limited success. One of the difficulties has been finding a vaccine to produce antibody to all of the components of the virulent organism, especially to the cytotoxin and to certain cell membrane associated proteins. Furthermore, it is believed that none of the prior art viruses have an adverse effect on the potentiation of P. haemolytica by bovine viral diarrhea virus (BVDV). Bovine viral diarrhea virus has been found to potentiate pasteurellosis, although the exact mechanism is unknown.
Another shortcoming of the prior art viruses has been administration. One vaccine is given intradermally, an unusual and very inconvenient method for vaccinating cattle. Other prior art vaccines sometimes produce marked swelling and abscessation at the site of vaccination in greater than 5% of the animals.